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I am working on following circuit involving BC107 NPN Philips TO-92 transistor and voltage source of 4.2 V.

schematic

simulate this circuit – Schematic created using CircuitLab

I got some confusion when measuring collector's current. I was expecting that to be at least 0.2 A but when I insert probes and measure current as shown in the picture I get a reading of 0.0079 A. That would mean an DC Gain (beta/hFE) of Ic/Ib=0.0079/0.0023=~3.37, while this transistor should yield a gain of about 40-200 (I do not have spec for TO-92 though, it's taken from datasheet for BC107 TO-18, can't find any spec for TO-92...).

I would like to understand why am I getting 0.0079 reading when the base current (Ib) is 0.00234 A (confirmed with multimeter).

Ib = (4.2 - 0.7) / 1480 = 0.0023

Ic (expected) = Ib * hFE = 0.0023 * [40:200] = [0.092:0.460] [A]

but real Ic = 0.0079 [A]

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  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. Any conclusions reached should be edited back into the question and/or any answer(s). \$\endgroup\$
    – Dave Tweed
    Commented Dec 23, 2018 at 17:29

1 Answer 1

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You appear to have the transistor connected backwards. Collector is grounded and emitter is used as a collector.

The transistor will work that way, but will have a really low beta, often in the range you are seeing. The Vceo breakdown will also be very low, but okay for your 5V supply. Image from this site.

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  • \$\begingroup\$ Yes, we've already fond I used wrong datasheet. Actually I can't find a datasheet for this supposedly "BC107/PH10440 PHILIPS (TO-92) PLASTIC NPN" and I think I will just put it on the shelf and get back to learning transistors using one I am more sure about. \$\endgroup\$
    – 4pie0
    Commented Dec 23, 2018 at 16:51
  • \$\begingroup\$ The Chinese often will take part numbers that point to a particular package and cavalierly re-use the part number for a different (more popular) package. I have reels of so-called 1N4004, 1N5819 diodes in surface mount packages, for example. When western companies re-used the part number for the hermetic 2N2222 for example, it was usually called something like PN2222 in TO-92, and the TO-92 2N3904, for example, became MMBT3904 in SOT-23. But that example has not been followed. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Dec 23, 2018 at 16:57
  • \$\begingroup\$ But the USA BJT's ( PN2222A ) will have a different pinout. \$\endgroup\$
    – G36
    Commented Dec 23, 2018 at 17:46
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    \$\begingroup\$ @G36. Yes, there are three common TO-92 pinouts. American (EBC) eg. 2N3904, European (CBE) eg. BC547 and Japanese (ECB) eg. 2SC1815. You can find parts like 8050 in more than one TO-92 pinout, just to keep you on your toes. Fortunately almost all SOT-23 BJT pinouts are the same. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Dec 23, 2018 at 17:55

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